This invention relates to aerosol dispensing containers incorporating a bag holding a product to be dispensed and a propellant chamber formed between the bag and container sidewall, and more particularly, to an improved grommet or fill valve (sometimes also referred to as an umbrella valve or seal valve) by which a propellant is introduced into the container and retained therein until all the product in the container is dispensed. Alternately, the container may employ a piston on one side of which is the product to be dispensed and on the other side of which is the propellant chamber. Again, the improved fill valve allows a propellant to be introduced into the chamber and retained therein until all the product is dispensed.
Certain types of aerosol containers include a collapsible bag or pouch disposed within the container. The bag or pouch is filled with a fluent material dispensed by the container. A propellant chamber is formed between the bag and container sidewall. At the base of the container, on a domed bottom surface thereof, an opening is formed and a fill valve is seated in this opening. During manufacture, after the bag or pouch is seated in the container and a dispensing valve attached to the top of the container, a propellant is injected into the container. For a 7 ounce container, 10-12 grams of a propellant such as butane is injected. To inject the propellant, the fill valve is unseated so propellant can flow into the chamber around the valve. The fill valve has a stem which fits through the opening, an inner sealing element formed on one end of the stem, and a “bowtie” section formed on the outer end of the stem. Opposed longitudinally extending grooves extend from the bowtie section along the side of the stem. During filling, a nozzle presses against the bowtie section of the valve and pushes the valve a sufficient distance inwardly that the butane can flow through the grooves into the chamber. In addition, pressure of the butane causes the valve to flex upwardly to create a larger opening for the gas to enter the container. When the nozzle is withdrawn, the pressure in the chamber now forces the inner sealing element of the fill valve against the inner surface of the container bottom, sealing the container. An example of this type of aerosol container is shown in co-assigned U.S. Pat. No. 5,915,595.
A second type container utilizes a piston disposed in the container with the product to be dispensed being on an outlet valve side of the piston, and the other side of the piston partially forming a propellant chamber in which the butane is injected. The propellant is introduced into the container through a fill valve fitted in the base of the container in the same manner as described above.
Many of the bag-in-can modalities and all piston cans require a bottom gassing, after which the entry hole in the can base for the injection of the gas must be hermetically plugged. A variety of grommets have been developed. Those include U.S. Pat. No. 4,658,979 by Mietz et al. (Hereinafter “Mietz”). Mietz discloses a basic umbrella-shaped grommet used for a pressurized dispensing container. The grommet includes umbrella sealing means located within the container, shoulder means located outside of the container, and stem means joining the umbrella sealing means and the shoulder means. U.S. Pat. No. 6,729,362 by Scheindel (Hereinafter “Scheindel”). Scheindel also discloses a grommet for a pressurized dispensing container. The grommet is characterized by a resilient neck portion which is extended during the injection of propellant so that a passageway for the propellant is formed around the neck. After the charging is completed, the neck contracts creating a tight sealing between the grommet and the container bottom. The grommet may be thermoset molded using buna-N or neoprene or other known material. The grommet may be injection molded.
There are number of problems with the currently used grommets, however, both with respect to their design and manufacture. Although a number of attempts have been made, existing types of grommets do not properly seal, allowing propellant to leak out of the container subsequent to filling. Propellant leakage dramatically reduces the usefulness of a container to dispense product, and if enough propellant leaks out, the result is a “dead” container. A “dead” container is one on which, when the outlet valve is actuated, little or no product is dispensed. It will be understood that there is usually a significant time between when a container is filled and it is used. During this period when the container is being packaged, shipped, warehoused, sits on a shelf in a store, and finally purchased, any loss of propellant, however small, will affect the final usefulness of the can. It has been estimated that even a small leak can result in the loss of as much as 1 gm. of propellant a year.
Other, related problems occur during manufacture of the fill valve. Heretofore, fill valves have been made using a compression molding process which has been found to result in poor sealing because of poor cross-linking of the molded material during the manufacturing process, and compression setting. Cross-linking is the formation of chemical links between molecular chains in polymers. Compression set is a property of grommets that adversely affects their sealing capability. The result has been that even if a fill valve properly seals after filling; over time, propellant can still escape from the container because of poor compression set.
In addition to these factors, another factor causing poor sealing is the cryogenic process used to remove flash produced on a grommet during compression molding. After the molding process is completed, the fill valves are frozen and any extraneous material (the flash) is knocked or broken off the part. However, the freezing process can result in large and/or microscopic cracks being created in the grommet and these cracks become leakage paths for propellant to escape from the container.
It will be appreciated by those skilled in the art, that release of the propellant to the atmosphere adds to our environmental problems, regardless of how the propellant escapes. In addition, one “band aid” fix to loss of propellant is to inject more propellant into the container during filling than is otherwise needed, so even if some propellant escapes there is still sufficient propellant that product is adequately dispensed from the container. Further, manufacturers, fillers, or suppliers of the containers often have to replace “dead” containers adding to their warranty costs.
Another problem with previous fill valves has been that molded into each fill valve is indicia identifying the particular mold and mold cavity in which the fill valve is formed. This, of course, is to assist in trouble shooting if valves are found to be defective. Currently, this indicia is in the form of raised alphanumeric characters on one surface of the fill valve. It has been found that after manufacture, when the fill valves are placed on a conveyor which moves them to a container assembly station, the raised characters often cause the valves to not move smoothly along the conveyor, but rather more haphazardly. This can require additional manpower to insure that the fill valves do properly get to the assembly station and are properly oriented for insertion into the bottom of a container.